The purpose of this grant proposal is to investigate role of thrombospondin (TSP) in hemostasis and cell adhesion. We will test the hypothesis that TSP polymers support cell adhesion whereas monomers bind fibrinogen and function to support platelet aggregation. The proposal will investigate the factors that effect TSP monomer-polymer conversions as well as biochemically characterize the different subunit forms of TSP. Additionally, we will characterize the platelet-TSP receptors by means of TSP- platelet binding studies, TSP-photoaffinity labeling studies, TSP affinity chromatography, and anti-TSP affinity chromatography, and anti-TSP monoclonal antibody production. We will investigate the role of TSP in clot formation and cell adhesion. Our ultimate goal is to discover by the use of monoclonal antibodies which molecular interactions of TSP play an important role in blood coagulation and cell adhesion.